Cellulose is an important constituent in plants and comprises anhydrous glucose units. When cellulose is depolymerised glucose may be obtained, which can be used for many different purposes including manufacture of ethanol using yeast.
The degradation of cellulose is complicated due to the resistibility of the material.
When cellulose is hydrolyzed with strong acid, by-products are formed which may act as inhibitors for the yeast in a subsequent step in the manufacture of ethanol. In order to achieve a total degradation of cellulose a long duration of the hydrolysis is required and during a prolonged hydrolysis dissolved cellulose may react further and form inhibitors for yeast.
Another approach is to degrade cellulose with enzymes. However the present enzymatic processes are expensive mainly because they are slow and that the enzymes are relatively expensive.
Yet another approach is hydrolysis with diluted acid. This approach also suffers from problems with slow degradation.
There are several known ways to dissolve cellulose for various applications including manufacture regenerated cellulosic fiber. Often expensive chemicals are used in such processes.
Zhao et al, in Biotechnology and Bioengineering, pp. 1320-1328, Vol. 99, No. 6, 2008 discloses treatment of wood fiber bundles with NaOH and NaOH/Urea. There is disclosed treatment with cold NaOH. The treated pulp is neutralized. Any cellulose which is dissolved in the NaOH solution is apparently not used further. It is disclosed that treatment with cold NaOH is advantageous. The yield is improved with pretreatment.
WO 2008/095098 discloses a process for the manufacture of sugar from biomass, where the biomass is pretreated with alkali solution to improve the following hydrolysis. The temperature is increased and is 50-150° C., preferably 80-140° C.
Jeihanipour et al, in Biorecource Technology, pp. 1007-1010, Vol. 100, 2009 discloses alkali pretreatment of cotton linter followed by enzymatic hydrolysis. It is disclosed that low temperatures improves the process. The cellulose material which is used is not dissolved or suspended in the alkali solution, it remains solid. A problem in this technology is that some of the cellulose material dissolves and is discarded, which reduces the yield.
EP 0 344 371 A1 discloses a method for the production of monosaccharides by hydrolysis of lignocellulosic materials. There is no dissolution of the cellulose, where the dissolved cellulose is recovered. The cellulose is washed, but cellulose that is dissolved is apparently not recovered.
U.S. Pat. No. 4,089,745 discloses a process for enzymatic conversion of corn hull cellulose to glucose. Again there is no dissolution of the cellulose, where the dissolved cellulose is recovered. The cellulose is washed, but cellulose that is dissolved is apparently not recovered.
US 2008/0102502 A1 concerns recovery of inorganic salt during processing of lignocellulosic feedstocks. It is mentioned that carbon dioxide can be used to adjust pH.
There is a need for an improved process for the degradation of cellulose.